Bulk-solidifying amorphous metal alloys (a.k.a. bulk metallic glasses) are those alloys that can form an amorphous phase upon cooling the melt at a rate of several hundred degrees Kelvin per second or lower. Most of the prior amorphous metal alloys based on iron (i.e., those that contain 50 atomic percent or higher iron content) are designed for magnetic applications. The Curie temperatures are typically in the range of about 200-300° C. Furthermore, these previously described amorphous iron alloys are obtained in the form of cylinder-shaped rods, usually three millimeters or smaller in diameter, as well as sheets less than one millimeter in thickness.
Recently, a class of bulk-solidifying iron-based amorphous metals have been described that exhibit suppressed magnetism, relative to conventional compositions, while still achieving acceptable processibility of the amorphous metal alloys and maintaining superior mechanical properties and good corrosion resistance properties. These alloys are described in U.S. patent application Ser. No. 10/364,123 and PCT Patent Application No. PCT/US03/04049, (the disclosures of which are hereby incorporated by reference). These previously described amorphous alloys, which are non-ferromagnetic at ambient temperature, are multicomponent systems that contain about 50 atomic percent iron as the major component. The remaining composition combines suitable mixtures of metalloids and other elements selected mainly from manganese, chromium, and refractory metals. In addition these amorphous alloys exhibited improved processibility relative to previously disclosed bulk-solidifying iron-based amorphous metals, and this improved processibility is attributed to the high reduced glass temperature Trg (e.g., 0.6 to 0.63) and large supercooled liquid region (ΔTx (e.g., about 50-100° C.) of the alloys. However, the largest diameter size of amorphous cylinder samples that could be obtained using these alloys was approximately 4 millimeters.
There is a strong desire for bulk-solidifying iron-based amorphous alloys, which are non-ferromagnetic at ambient temperature and exhibit a higher degree of processibility than previously disclosed alloys. The present invention relates to amorphous steel alloys that comprise large atom inclusions to provide a non-ferromagnetic (at ambient temperature) bulk-solidifying iron-based amorphous alloys with enhanced glass formability. Large atoms are characterized by an atom size ratio of ˜1.3 between the large atom and iron atom, and their inclusion in the alloy significantly improves the processibility of the resulting amorphous steel alloy, resulting in sample dimensions that reach 12 millimeters or larger (0.5 inch) in diameter thickness.